1. Field of the Invention
The present invention relates generally to the field of magnetic read/write heads and magnetic data storage, and more particularly, to a shield structure for a shielding a read sensor in the lateral or cross-track direction to reduce side reading.
2. Relevant Background
Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, and hard disk. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information. Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. Data on magnetic media is often stored in a line or track. Magnetic media often have multiple tracks. In the case of disks, the tracks are nested annular rings with more bits per track and more tracks per disk increasing data density. Data density or areal density, therefore, is determined by both the bit length and by the width of the bit. To decrease bit size, head size is decreased by fabricating thin film read and write heads.
Ongoing, important goals of researchers in magnetic recording technology include producing disk drive read heads that achieve strong signals, providing accurate readback of those signals, minimizing noise interference, and providing very high areal density while controlling manufacturing costs. Unfortunately, some of these goals directly conflict with one another. For example, to achieve ever-higher areal densities, track widths on a disk become smaller necessitating that the components used to read and write data also become smaller, which makes manufacturing more difficult and expensive.
High density recording, such as over 100 Gbit/in2, requires a highly sensitive read head. At higher densities, resistance changes in the head originating from the giant magnetoresistive (GMR) effect are reduced based on the progressively smaller dimensions of the length of the read head. The GMR effect (as well as the MR effect) is the measure of changes in electrical resistance of magnetically soft material, with the GMR effect found specifically in thin film materials systems. In current-in-plane (CIP) read heads, electrical current flows between contacts parallel to the disk or media surface through a GMR element or a read sensor with changes in resistance detected by voltage changes (i.e., readback voltage or output signal). More sensitive read heads have current flows through the films or GMR elements perpendicular (CPP) to the long axis of the structure and normal to the disk or media surface. The sensitivity of the CPP read heads has recently been further enhanced by building CPP read head structures that utilize tunneling magnetoresistance (TMR) concepts in which electrons “tunnel” through very thin insulators based on the magnetization of layers above and below the insulator.
One problem associated with using CIP and CPP read heads is directly related to reduced track widths and head size. Side reading occurs when a read sensor receives noise or stray signals from tracks adjacent the track being read by the read sensor and has become a bigger problem as the tracks have been placed closer together. Traditional head design that uses a permanent magnet abutted junction is typically adequate for larger track widths but as the track widths decrease the magnitude of the output signal or readback voltage weakens while at the same time the unwanted signals from adjacent data tracks yields more and more severe interference. The increased side reading of the read sensor results in degraded read data integrity. Achieving a high recording density requires a narrow head track width while maintaining the readback voltage output. Presently, the magnetic read width decreases have not scaled linearly with reductions to very narrow track widths (such more than 50,000 tracks per inch (TPI)). For example, recent studies have shown an almost 30 percent reduction in physical read width from 0.16 micrometers to 0.11 micrometers while magnetic widths have only changed by a small fraction of this amount. Prior efforts to shield the read sensor, such as in the track direction, have not been entirely successful and have even caused a sharpening of the readback voltage waveform (as measured by PW50 which is a pulse width measurement made at a 50 percent voltage level of the readback pulse), while the goal is to reduce the pulse width measurement to provide a read head able to read narrow pulses having a minimum interaction with each other.
Hence, there remains a need for a read head capable of effectively reading narrower track widths or having a narrower read back width (MRW). Such a read head preferably would provide improved control over noise from adjacent tracks including effects of side reading and would produce reduced PW50 measurements and would be suitable for manufacture using existing technologies including existing lithography processes.